The invention relates to a plug for sealing substances in holes drilled in wooden structures, particularly for sealing wood preservative in holes drilled in standing wood utility poles.
Exceedingly large numbers of standing wooden poles are used by power and communications utilities. To prolong the life of these poles, wood preservative is injected into holes drilled in the pole, which tends to reduce the spread of rot within the pole. Usually, the first internal rot treatment is applied after the pole has been in service for a number of years, and additional treatments are applied at regular intervals. The holes drilled into the wood structures are usually sealed with wooden dowels or plugs which are hammered into the holes after the treatment. When additional treatment is required the wood plugs are removed from the hole, and this can present some difficulty. The dowel can be damaged when being removed from an opening, and commonly it cannot be reused, and thus another dowel is required. Also, old wooden dowels split, and can fall from the opening with the risk of contaminating the immediate area with wood preservative, which can be highly toxic. After many years, the utility pole may have been treated several times, and each time a separate hole might be required, each hole having a separate plug. Installation and maintenance of many plugs is time consuming, and also increases the risk of inadvertent loss of a plug from an opening.
It is known to provide specially adapted threaded plugs to plug openings in treated poles or trees. Typical examples are found in U.S. Pat. Nos. 3,968,594 issued to Kawakami and 4,724,793 issued to Sletten. Both of these patents disclose tapered plugs having threads on the outer periphery thereof, with a central opening extending through the plug. An orifice is provided adjacent the thread or tip of each plug, the orifice communicating with the central opening of the plug to distribute chemicals into the wood. It would appear that both these plugs are fabricated from a rigid material, and require screwing in and screwing out, which can be a time consuming process.